This application claims priority of DE 198 51 746.7, filed Nov. 10, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a transfer system having the characteristics of the preamble of claim 1.
Transfer systems are required, for example, in the case of vehicle body presses. Vehicle body parts are manufactured from metal sheets in several successive forming steps. For this purpose, the vehicle body presses have several press stations which operate at the same stroke rate. When the tools of the individual press stations open up, the workpieces must be transferred in order to be fed to the respective next machining stage. Transfer systems are used for this purpose.
Such a transfer system is known from German Patent Document DE 41 43 099 A1. This transfer systems has so-called suction bridges which are formed by a cross member with vacuum-operated suction devices provided thereon. These suction devices are set up for receiving the sheet metal parts and releasing them again in a controlled manner. The suction bridges are held on both ends on the travelling carriages which are movably disposed on guide rails. The guide rails extend in parallel and at a distance from one another through the whole length of a transfer press. For the workpiece transport, the suction bridges move into opened tools, receive a workpiece and move these to an intermediate deposit or receive the workpieces in the intermediate deposit and move into the opened next tool. For driving the travelling carriages, a linkage is provided which leads to a cam drive. This cam drive is connected with the main press drive. A lifting and lowering movement is superimposed to the back-and-forth movement of the transfer rails achieved in this manner. This lifting and lowering movement is generated in that the guide rails as a whole are lifted and lowered. The stroke units are used for this purpose.
Such a transfer system moves the suction bridges connected with a cam drive in a synchronous manner. Correspondingly, the participating tools must simultaneously open and close.
A more flexible transfer system is desirable in many cases.
A modular transfer system is known from International Patent Document WO 93/0185. Between individual press stations, transfer modules are arranged which can be controlled independently of one another. Each transfer module includes a suction bridge whose carrier element extends transversely to the transport direction in a horizontal manner. On its two ends, the carrier element is carried by drive units. The drive units are constructed symmetrically to one another. Each drive unit contains a stroke unit which is disposed in a stationary manner and generates a linear lifting and lowering movement. This lifting and lowering movement is transmitted directly to the carrier element. A crank mechanism is arranged between the stroke unit and the carrier element and has the purpose of causing a movement of the suction bridge in the transport direction. The crank mechanism is formed by a double crank in conjunction with a planetary transmission. The cranks of the crank mechanism and the gear wheels of the planetary transmission can be rotated or swivelled about mutually parallel vertical axes. This results in considerable tilting stress for the individual bearings and articulations of the crank mechanism which may result in problems concerning wear and precision. In addition, during their swivel movement about vertical axes of rotation, the cranks swivel out to the side. A corresponding space has to be kept open for this purpose, which represents a certain limitation.
Based on the above, it is an object of the invention to provide a transfer system which utilizes space existing in a transfer press and has a construction which is as space-saving as possible.
This object is achieved by means of a transfer system having the characteristics of claim 1.
The transfer system according to the invention has a modular construction and contains several mutually independently controllable transfer modules. Each transfer module is arranged between two stations of the transfer press or other system. The stations may be press stages or other machining or orienting stations.
As the result of the independent controllability of the transfer modules, it is possible to cause press stations to operate in a time-staggered manner.
The workpiece holding devices, which are formed, for example, by suction bridges, are guided by a swivel arm which is disposed to be swivellable about a swivelling axis. The arrangement of the swivelling axis according to the invention xe2x80x94deviating from the vertical line and preferably horizontal xe2x80x94permits a compact construction of the press.
The drive of the swivel arm contains a combination of a linear drive and a rotary or swivel drive. It is endeavored to construct a multi-station press to be as short as possible. For this reason, it is attempted to set up the individual press stations or the corresponding tables at a distance from one another that is as small as possible. The smallest possible distance is defined by the space requirement of the press stands if sliding tables between the press stands are to be moved laterally to the outside. For this reasons, the press stands are not very wide. The space for the transfer modules arranged here is correspondingly small. By means of the combination of the linear drive and the swivel drive, it becomes possible to utilize this space well. For example, only a single linear drive, which is relatively narrow, has to be arranged on a press stand. The swivel drive may be arranged on a linear slide block moved by the linear drive, whereby no additional space requirement is created in the transport direction.
The arrangement of the swivelling axis of the swivel arm according to the invention has the result that the swivel arm can take up a vertical position in which it is virtually in parallel to the press stands and also in parallel to the working direction of the press slides. In this position, the space requirement is minimal. When the tools open and a transfer stroke is to be carried out, the swivel arm will swivel out to the tool which is disposed in front or behind it in the transport direction. However, in this case, the swivel arm does not carry out a laterally projecting movement or other movement which may lead to a collision with the tool or with parts of the press. In the parking position (vertical swivel arm) as well as in the maximally projecting position (swivel arm is diagonally inclined) as well as in all intermediate positions, the space requirement of the transfer module will remain modest.
The essentially horizontal arrangement of the swivelling axis and of the axis of rotation of the output shaft of the swivel drive have the result that the loads occurring on the swivel arm occur at the corresponding bearing points as a radial load and not as tilting stress. This results in a precise guidance of the workpiece holding device by the swivel arm or arms and to moderate bearing reaction forces. This, in turn, permits a relatively light bearing design and correspondingly high dynamics of the transfer module while the positioning precision is good and the wear is low because of little stress to the material.
The transfer module is preferably constructed with two axes and thus defines a transfer curve which extends in a flat plane. This may, for example, be an imaginary vertical plane extending in the transport direction. The transfer curve K contains only movement components in the transfer direction and, in addition, in the vertical direction. In this case, the swivelling axes of the swivel arms may be oriented transversely to the transport direction. If a lateral offset of the workpieces is desired during the passage through successive press stations, the swivelling axes of the swivel arms may also be arranged at an angle which differs from 90xc2x0 transversely to the transport direction. The angular position can be adjusted as required.
In addition, the swivelling axis is oriented preferably at a right angle with respect to the movement direction of the linear drive, which preferably operates in the vertical direction. Thus, the dynamic stressing of the linear guide, which occurs predominantly as the result of the acceleration and braking of the workpieces, is absorbed by the lateral guidance of the slide block provided on the linear guide and acts little or not at all upon the stroke drive. Simultaneously, the dynamic bearing reactions on the swivelling axes are oriented in the radial direction. On the whole, a precise as well as statically and dynamically favorable construction is therefore achieved. Different implementation possibilities are obtained. The linear drive may, for example, be disposed in a stationary manner, while the swivel drive is arranged, for example, on a slide block driven by the linear drive. The swivel drive may drive the swivel arm directly. For a movement of the workpiece holding device in the transport direction without a lifting and lowering component, the controlling of both drives will then be required. As an alternative, it is possible to swivellably dispose the swivel arm on a second slide block which is not driven and which can be displaced in parallel to the former slide block or in an alignment therewith. The swivel drive operates the swivel arm, for example, by way of a guide rod. If the guide rod is half as long as the swivel arm and is applied to its center, an uncoupling of the movement is obtained. The swivel drive will then cause only an advance in the transport direction, while the stroke unit causes only the lifting and lowering of the workpiece holding device.
Additional alternative constructions are conceivable. The swivel drive can, for example, be disposed in a stationary manner and the swivel arm may have a telescoping construction. The linear drive will then form the telescope drive. As required, a weight compensation device can be provided on the transfer module which keeps one, several or all drives free of weights. The weight compensation device may, for example, by formed by a force generator (pneumatic cylinder), which, at a suitable point, introduces a force into the transmission carrying the workpiece holding device, which transmission is constructed, for example, as a lever mechanism.
Details of advantageous embodiments of the invention are the object of subclaims, are indicated in the drawing and/or the pertaining description.